The present invention relates to a device for determination of a pulsating air mass flow in an internal combustion engine, particularly in the air induction manifold of the engine.
Devices for determination of a pulsating air mass flow are known which include a sensor producing an output signal to be evaluated for determination of the air mass flow which is fed to a filter device.
In the case of an internal combustion engine, it is known for the operating parameters which normally have to be detected, for example the induction manifold pressure or the induction air mass flow, to fluctuate in time with the internal combustion engine. In addition, when using an air flowmeter to measure the induction air mass flow, noise occurs which has a number of causes. On the one hand, the air flow contains noise which is caused by turbulent fluctuating movements. This noise could be suppressed, for example, by averaging in the time domain and/or space domain. However, such averaging would not take account of the dynamic processes which occur in particular as a result of a sudden change in the air mass flow during acceleration and as a result of induction manifold pulsations in certain operating conditions.
A second noise source which has an adverse effect on the output signal is the electronic noise which is caused by electromagnetic interference. This noise must also be reduced using suitable means in order that reliable signal evaluation is possible.
In order to reduce the influence of noise and other disturbances in the evaluation of a signal from an air flowmeter, EP-0 429 819 B1 proposes that the output signal, which fluctuates cyclically in time with the internal combustion engine, of an induction manifold pressure sensor or of an air flowmeter be filtered before further processing. In this case, a band rejection filter is used to filter the cyclically fluctuating variable and is designed such that a signal appears at its output which signal reproduces the mean value of the cyclically fluctuating variable as well as possible dynamically. An adaptable center frequency of the band rejection filter is used for this purpose, the center frequency of the band rejection filter in this case varying, for example, as a function of rotation speed values determined in advance. Overall, it is proposed that the center frequency be set such that adequate attenuation of the cyclic fluctuation of the signal is achieved, so that an output signal corresponding to the mean value is produced directly at the output of the bandpass filter.
The known signal filtering has the disadvantage that a mean-value error nevertheless occurs during the process of averaging a severely fluctuating signal. This cannot be ignored, particularly in the case of air flowmeters having a curved characteristic, for example, thermal air flowmetering. Thus, in the case of thermally fast air flowmeters, the cyclically fluctuating signal elements must not be filtered out.